The present embodiments relate to medical diagnostic ultrasonic imaging, and in particular, to systems that adaptively set one or more stages of back-end mapping that may include gain, dynamic range and post-processing map stages to improve such imaging.
In conventional ultrasonic imaging, a B-mode signal is adjusted for gain and dynamic range before the B-mode signal is mapped to a range of gray levels or colors for display. The dynamic range of the signal to be displayed can conventionally be set by the user by a display dynamic range control. This control is conventionally independent of range and azimuthal position in the image. The gain can conventionally be varied by the user using depth gain compensation (DGC) or time gain compensation (TGC) control along with the master gain or B gain control. The DGC and TGC controls are conventionally variable in range (axial dimension) only, and the master gain is independent of both range and lateral (azimuthal) position. A few systems also offer lateral gain compensation in addition to depth gain compensation, but the two one-dimensional gain controls comprise only an approximation to a true two-dimensional gain control.
After gain and display dynamic range have been applied, log-compressed B-mode signals are re-quantized, typically to 8-bit or 256 quantization levels. The quantization step (in dB) is given by the ratio of the dynamic range selected by the user to the number of quantization levels.
After quantization, a post-processing map is used to map the quantization levels to a range of gray levels or colors. This map can be a selected one of a predesigned set of maps or alternately a user-designed map. These maps are also conventionally range and azimuth independent.
On commercially available ultrasound imaging systems, gain controls are often used by the users to adjust the brightness level. In many cases, users adjust the gain mainly to keep the regional mean of the soft tissue gray level within a narrow range of gray values across the image. This preferred range is consistent from user to user, and in many cases users tend to adjust the gain to set the gray level for soft tissue roughly to the 64th gray level on a linear map that maps 0 to black and 255 to white.
The gain adjustments may work well for two-dimensional imaging given the user interface. Overall gain is controlled by a knob or single setting applied to all data. TGC or DGC are controlled by sliders representative of different depths. However, spatial variation in three-dimensions is difficult to implement on a user interface.
U.S. Pat. No. 6,579,238 discloses various embodiments for automatically setting the gain, dynamic range, and mapping. These parameters may be optimized by fitting a surface for imaging.